Broad-spectrum A1(1-x-y)InyGaxN light emitting diodes and solid state white light emitting devices

ABSTRACT

A broad-spectrum Al (1-x-y) In y Ga x N light emitting diode (LED), including: a substrate, a buffer layer, an N-type cladding layer, at least one quantum dot emitting layer, and a P-type cladding layer. The buffer layer is disposed over the substrate. The N-type cladding layer is disposed over the buffer layer to supply electrons. The quantum dot emitting layer is disposed over the N-type cladding layer and includes plural quantum dots. The dimensions and indium content of the quantum dots are manipulated to result in uneven distribution of character distribution of the quantum dots so as to increase the FWHM of the emission wavelength of the quantum dot emitting layer. The P-type cladding layer is disposed over the quantum dot emitting layer to supply holes. A broad-spectrum Al (1-x-y) In y Ga x N yellow LED may thus be made from the LED structure of this invention, with an emission wavelength at maximum luminous intensity falling within a range of 530˜600 nm, and FWHM within a range of 20˜150 nm. After packaging an Al (1-x-y) In y Ga x N blue LED to form a solid state white light emitting device, the mixing of blue light and yellow light would generate white light with a high CRI index, high luminous intensity and capable of various color temperature modulation.

FIELD OF THE INVENTION

This invention relates to a light-emitting diode (LED) and a solid statewhite light emitting device, more particularly to a broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N LED and a solid state white light emittingdevice.

BACKGROUND OF THE INVENTION

The rapid development of nitrides emitting devices in recent years hasresulted in high demands in high brightness LED, such as backlight usedin mobile phones, indicators, and outdoor display panels. Along with thesignificant enhancement in emission efficiency, high interest andexpectation is given to the use of high brightness LED to serve as awhite light source. Presently, the structures using high brightness LEDto serve as white light sources include the followings:

The first structure is developed by Nichia Kagaku Kogyo KabushikiKaisha, where yellow fluorescent powder (YAG: Ce; Y₃Al₅O₁₂: Ce³⁺) isadded into blue LED to generate mixed white light (with reference toU.S. Pat. No. 6,069,440). Such a structure provides a white lightemitting device that is of the lowest cost among the commerciallyavailable white light emitting devices. However, because of the bluehalo effect, the reducing reliability and low light conversionefficiency of fluorescent powder, and the limited emission efficiencydue to the use of a single LED, such a structure cannot attain a whitelight emitting devices with high color saturation, high luminousintensity, high reliability and capable of various color temperaturemodulation.

The second structure was recently developed and aimed at improving thepoor color rendering index (CRI) of the aforementioned white lightsource, where ultraviolet A (UVA) was excited to generate red, green andblue fluorescent powder, for producing white light sources with a highCRI index (with reference to U.S. Pat. Nos. 6,592,780; 6,580,097 and6,596,195). Such a structure involves the drawbacks of poor reliabilityin the mixture of RGB fluorescent powder. In addition, the light sourcegenerated from exciting UVA cannot serve as a mixed light source,thereby resulting in an even lower luminous intensity. Furthermore, sucha structure further needs to overcome the safety concerns of resindeterioration and UVA leakage during the packaging process.

The third structure is one of high cost, which joins plural emittingdevices to generate high brightness, thereby attaining a white lightsource with an excellent CRI (with reference to U.S. Pat. No.6,563,139). However, the commercially available package attained fromsuch a structure is limited to that including red-orange-yellow lightAlGaInP LED and nitrides blue LED with a wavelength greater than 580 nm.As such, the drawbacks of such a structure includes the high costinvolved in packaging multiple chips, and difficulty involved inpackaging the two LEDs of different characteristics, such as thermalstability, driving voltages and material reliability.

In addition, others also suggest the use of plural quantum wells withdifferent wave bands in a single chip to directly generate white light(with reference to JP2001-028458). However, the process formanufacturing such a device and the emission efficiency of such a devicecannot meet the performance demands of commercial white light. A furtheralternative is to use an Al_((1-x-y))In_(y)Ga_(x)N blue light chip toexcite AlGaInP for generating yellow light that is then mixed togenerate a white light source. However, the low luminous intensity andnarrow bandwidth of the yellow light results in poor lighting effects.Yet another alterative is to use ZnSe as the luminescent material (withreference to U.S. Pat. No. 6,337,536). However, the reliability, colorsaturation, luminous intensity of such is inferior to a white lightemitting device of the Al_((1-x-y))In_(y)Ga_(x)N type.

Thus, there has been a need for a novel LED and a solid state whitelight emitting device capable of resolving the above drawbacks.

SUMMARY OF THE INVENTION

It is thus an object of this invention to provide a broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N LED, comprising: a substrate, a buffer layer,an N-type cladding layer, at least one quantum dot emitting layer, and aP-type cladding layer. The buffer layer is disposed over the substrate.The N-type cladding layer is disposed over the buffer layer and servesto supply electrons. The quantum dot emitting layer is disposed over theN-type cladding layer. The quantum dot emitting layer includes pluralquantum dots with an uneven character distribution so as to increase theFWHM (Full Width-Half Maximum) of the emission wavelength of the quantumdot emitting layer. The P-type cladding layer is disposed over thequantum dot emitting layer and serves to supply holes.

A broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N yellow LED may thus be madefrom the LED laminar structure of this invention, with an emissionwavelength at maximum luminous intensity falling within a range of530˜600 nm, and FWHM within a range of 20˜150 nm. After packaging withan Al_((1-x-y))In_(y)Ga_(x)N blue LED to form a solid state white lightemitting device, the mixing of blue light with yellow light wouldgenerate white light with a high CRI index, high luminous intensity, andcapable of various color temperature modulation. Since thebroad-spectrum emission bandwidth covers the visible spectrum that thehuman eyes are most sensitive to, this invention significantly enhancesthe luminous intensity of the white light. The distribution of thebroad-spectrum also further increases the CRI index and enhances thevarious color temperature modulation.

In packaging process, because blue and yellow LED implemented by thesolid state white light emitting device of this invention are both madeof Al_((1-x-y))In_(y)Ga_(x)N, they have similar driving voltages,thermal stability, reliability and ESD impedance characteristics, forsignificantly reducing the packaging cost and improving the reliabilityof the packaged devices.

Accordingly, the solid state white light emitting device of thisinvention may be implemented to serve as or to replace the white lightemitting device that is available in the commercial market, such as thewhite backlight of portable electronic products, vehicular lighting,landscape lighting, decorative lighting, and handheld lightingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other modifications and advantages will become even moreapparent from the following detained description of a preferredembodiment of the invention and from the drawings in which:

FIG. 1 is a schematic view illustrating the laminar structure of abroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED according to a firstembodiment of this invention;

FIG. 2 is a schematic view illustrating the laminar structure of abroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED according to a secondembodiment of this invention;

FIG. 3 is a schematic view illustrating the laminar structure of abroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED according to a thirdembodiment of this invention;

FIG. 4 is a schematic view illustrating the laminar structure of abroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED according to a fourthembodiment of this invention;

FIG. 5 a schematic view illustrating the laminar structure of a solidstate white light emitting device according to this invention;

FIG. 6 a schematic view illustrating the overall laminar structure of asolid state white light emitting device according to this inventionafter packaging;

FIG. 7 is a graph illustrating the luminous intensity and bandwidthdistribution of the solid state white light emitting device according tothis invention;

FIG. 8 is a graph illustrating the white light spectrum generated by thesolid state white light emitting device according to this invention;

FIG. 9 is a graph illustrating the white light spectrum generated by aconventional solid state white light emitting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made to the accompanied drawings for explaining theembodiments of LED and solid state white light emitting devicesaccording to this invention embodiment. In the drawings, identical orsimilar parts are identified by identical or similar reference numerals.In addition, the drawings are for illustrative purpose only, where thedimensions and proportions of the laminar structure as illustrated maybe different from the dimensions of the actual laminar structure.

FIG. 1 illiterates the laminar structure of a first embodiment for anbroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 10 according to thisinvention. The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 10comprises: a substrate 11, a buffer layer 12, an N-type cladding layer13, a quantum dot emitting layer 14 and a P-type cladding layer 15. TheAl_((1-x-y))In_(y)Ga_(x)N LED 10 further comprise two electrodes 16, 17to be connected to external power sources. The buffer layer 12 isdisposed over the substrate 11. The N-type cladding layer 13 is disposedover the buffer layer 12 and serves to supply electrons. The P-typecladding layer 15 is disposed over the quantum dot emitting layer 14 andserves to supply holes. The buffer layer 12, the N-type cladding layer13 and the P-type cladding layer 15 are all laminations made ofAl_((1-x-y))In_(y)Ga_(x)N.

The quantum dot emitting layer 14 is disposed over the N-type claddinglayer 13. The quantum dot emitting layer 14 includes plural quantum dots141, 142 and 143 of different dimensions. For example, the quantum dots141 are of the largest dimensions, the quantum dots 142 theintermediate, and the quantum dots 143 the smallest, to result in anuneven character distribution of the quantum dots, so as to increase theFWHM of the emission wavelength of the quantum dot emitting layer 14.

The quantum dot emitting layer 14 further comprises: a first barrierlayer 144 and a second barrier layer 145. The first barrier layer 144 isdisposed under the quantum dots and the second barrier layer 145 isdisposed over the quantum dots. The first barrier layer 144 and secondbarrier layer 145 are both laminations made ofAl_((1-x-y))In_(y)Ga_(x)N. The first barrier layer 144 and secondbarrier layer 145 each have an energy band gap that is greater than anenergy band gap of the quantum dots.

Normally, the first energy band gap 144 is further disposed over theN-type cladding layer 13 and the P-type cladding layer 15 is disposedover second barrier layer 145. Alternatively, the first barrier layer144 may be of a laminar structure identical to that of the N-typecladding layer 13 so as to become a part of the N-type cladding layer13. Similarly, the second barrier layer 145 may be of a laminarstructure identical to that of the P-type cladding layer 15 so as tobecome a part of the P-type cladding layer 15.

In the past, LED mostly uses quantum wells to modulate its wavelength.The Al_((1-x-y))In_(y)Ga_(x)N being asymmetrical crystalline inducessignificant piezo effects due to the asymmetry along C-axis. Thus,though increasing indium content in and thickness of the quantum wellwould result in increasing wavelength, such measures would alsosignificantly reduce its emission efficiency. Thus, in implementing theconventional quantum well emitting layer in the emitting layer made ofAl_((1-x-y))In_(y)Ga_(x)N, the drawback of significantly reducedemission efficiency will be observed upon increasing its emissionbandwidth to more than 540 nm by increasing the indium content in or thewidth of the quantum well. Thus, this invention implements the epitaxystructure of the quantum dot emitting layer in increasing the emissionefficiency of Al_((1-x-y))In_(y)Ga_(x)N LED under a long wavelength.

Quantum dots use the three-dimensional island formed from latticemismatch to serve as the carrier boundary in the three-dimensionalspace. Because the theoretical wavelength of Al_((1-x-y))In_(y)Ga_(x)Ncovers the spectrum from far UVA to red light, and because the FWHM ofthe emission wavelength of the quantum dot emitting layer may bemanipulated by the dimensions of the quantum dots or the indium contentin the quantum dots, the modulation of the dimensions of the quantumdots or indium content in the quantum dots is capable of manipulatingthe quantum dots to attain an uneven character distribution of thequantum dots so as to attain a broad-spectrum Al_((1-x-y))In_(y)Ga_(x)NLED 10. A yellow LED made from such an LED would have an emissionwavelength at maximum luminous intensity falling within a range of530˜600 μm, and FWHM falling within a range of 20˜150 nm.

With reference to FIG. 7, the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)NLED 10 of this invention may be implemented in generating yellow light,such that the emission wavelength at its maximum luminous intensity (of1) is 585 nm and its FWHM (Full Width-Half Maximum, that is, thewavelength bandwidth at an intensity of 0.5) is 90 nm (a bandwidth of540˜630 nm) so as to feature the LED with a broad-spectrum. Because thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 10 of this invention may bemanipulated to result in an uneven character distribution of the quantumdots, the emission wavelength may be modulated to a maximum luminousintensity and FWHM so as to feature the LED with a broad-spectrum.

As described above, the FWHM of the emission wavelength of the quantumdot emitting layer may be manipulated by the dimensions of the quantumdots or the indium content in the quantum dots. Though the firstembodiment of this invention adopts a single layer of quantum dotemitting laminar structure, this invention is not limited to theadoption of a single layer of quantum dot emitting laminar structure.FIG. 2 illustrates the laminar structure of a second embodiment for anbroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 20 according to thisinvention. In FIG. 2, parts that are of structures identical to those inthe first embodiment are designated by the same reference numerals, andserve the same functions if not specifically described.

The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 20 according to thesecond embodiment of this invention comprises: three quantum dotemitting layers 21, 22, 23, the quantum dot emitting layers each havingplural quantum dots. The first quantum dot emitting layer 21 includesplural quantum dots 211, 212; the second quantum dot emitting layer 22includes plural quantum dots 221, 222; and the third quantum dotemitting layer 23 includes plural quantum dots 231, 232. The LED is suchdesigned so that the dimensions of the quantum dots within a singlelayer are the same, but are different from the dimensions of the quantumdots in different layers. That is, the plural quantum dots 231, 232 ofthe third quantum dot emitting layer 23 are of the same dimension, butthe dimension of the plural quantum dots 231, 232 of the third quantumdot emitting layer 23 is greater than the dimensions of the quantum dots221, 222 of the second quantum dot emitting layer 22.

As exemplified by the first quantum dot emitting layer 21, the quantumdot emitting layer 21 further comprises: a first barrier layer 213 and asecond barrier layer 214. The first barrier layer 213 is disposed underthe quantum dots 211, 212; the second barrier layer 214 is disposed overthe quantum dots 211, 212. The first barrier layer 213 and secondbarrier layer 214 are both laminations made ofAl_((1-x-y))In_(y)Ga_(x)N. The first barrier layer 213 and secondbarrier layer 214 each have an energy band gap that is greater than anenergy band gap of the quantum dots.

The second quantum dot emitting layer 22 also comprises: a first barrierlayer 223 and a second barrier layer 224. The first barrier layer 223 ofthe second quantum dot emitting layer 22 is disposed over the secondbarrier layer 214 of the first quantum dot emitting layer 21. Becausefirst barrier layer 223 of the second quantum dot emitting layer 22 andthe second barrier layer 214 of the first quantum dot emitting layer 21are both laminations made of Al_((1-x-y))In_(y)Ga_(x)N, either the firstbarrier layer 223 of the second quantum dot emitting layer 22 or thesecond barrier layer 214 of the first quantum dot emitting layer 21 maybe omitted, such that only a single barrier layer is disposed betweenthe quantum dots 211, 212 of the first quantum dot emitting layer 21 andthe quantum dots 221, 222 of the second quantum dot emitting layer 22.

Thus, in a laminar structure having multiple quantum dot emittinglayers, two adjacent quantum dot emitting layers may be disposed withone or two barrier layers therebetween. In addition, the laminarstructure of the barrier layer may be manipulated to have differentproportions of Al_((1-x-y))In_(y)Ga_(x)N content, such that the twoadjacent quantum dot emitting layers may be disposed with two or morebarrier layers therebetween. So long as the barrier layers each have anenergy band gap that is greater than the energy band gap of the quantumdots, the two adjacent quantum dot emitting layers may be disposed withmore than one barrier layer therebetween.

The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 20 according to thesecond embodiment of this invention adopts a laminar structure havingmultiple quantum dot emitting layers, where the dimensions of thequantum dots of different quantum dot emitting layers differ from eachother to result in an uneven character distribution of the multiplequantum dot emitting layers, thereby achieving the same effect ofincreasing the FWHM of the emission wavelength of the LED 20.

FIG. 3 illiterates the laminar structure of a third embodiment for anbroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 30 according to thisinvention. The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 30 accordingto the third embodiment of this invention comprises three quantum dotemitting layers 31, 32, 33. The quantum dot emitting layers each haveplural quantum dots. The first quantum dot emitting layer 31 includesplural quantum dots 311, 312; the second quantum dot emitting layer 32includes plural quantum dots 321, 322; the third quantum dot emittinglayer 33 includes plural quantum dots 331, 332. The dimensions of all ofthe quantum dots are the same but the indium content within the quantumdots of different quantum dot emitting layers or within each of theindividual quantum dots is different. For example, the plural quantumdots 311, 312 of the first quantum dot emitting layer 31 include 30% ofindium content; the plural quantum dots 321, 322 of the second quantumdot emitting layer 32 include 40% of indium content; the plural quantumdots 331, 332 of the third quantum dot emitting layer 33 include 50% ofindium content. Summarily, the different indium content within thequantum dots of different quantum dot emitting layers results in anuneven character distribution of the quantum dots of different quantumdot emitting layers, and is thus capable of increasing the FWHM of theemission wavelength of the LED 30.

As exemplified by the first quantum dot emitting layer 31, the quantumdot emitting layer 31 further comprises: a first barrier layer 313 and asecond barrier layer 314. The first barrier layer 313 is disposed underthe quantum dots 311, 312; the second barrier layer 314 is disposed overthe quantum dots 311, 312. The first barrier layer 313 and secondbarrier layer 314 are both laminations made ofAl_((1-x-y))In_(y)Ga_(x)N. The barrier layer 313 and second barrierlayer 314 each have an energy band gap that is greater than an energyband gap of the quantum dots 311, 312.

FIG. 3 illiterates the laminar structure of a fourth embodiment for anbroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED 40 according to thisinvention. The Al_((1-x-y))In_(y)Ga_(x)N LED 40 according to the fourthembodiment of this invention comprises three quantum dot emitting layers41, 42, 43. The quantum dot emitting layers each include plural quantumdots. As exemplified by the first quantum dot emitting layer 41, thefirst quantum dot emitting layer 41 includes plural quantum dots 411,412, 413 of different dimensions. For example, the dimensions of thequantum dots 411 are greater than those of the quantum dots 412; and thedimensions of the quantum dots 412 are greater than those of the quantumdots 413. In this embodiment, the dimensions of the quantum dots ofdifferent quantum dot emitting layers differ from each other to resultin an uneven character distribution of the multiple quantum dot emittinglayers, thereby achieving the same effect of increasing the FWHM of theemission wavelength of the LED 40.

As exemplified by the first quantum dot emitting layer 41, the quantumdot emitting layer 41 further comprises: a first barrier layer 414 and asecond barrier layer 415. The first barrier layer 414 is disposed underthe quantum dots 411, 412, 413; the second barrier layer 415 is disposedover the quantum dots 411, 412, 413. The first barrier layer 414 andsecond barrier layer 415 are both laminations made ofAl_((1-x-y))In_(y)Ga_(x)N. The first barrier layer 414 and secondbarrier layer 415 each have an energy band gap that is greater than anenergy band gap of the quantum dots 411, 412, 413.

In the first to fourth embodiments described above, either the measureof varying the dimensions of quantum dots or the measure of varying theindium content within the quantum dots is implemented to result in anuneven character distribution of the quantum dot emitting layers, so asto achieve the effect of increasing the FWHM of the emission wavelength.However, according to this invention, the indium content within thequantum dots may also differ with the dimensions of the quantum dotsbeing different from each other, such as the embodiments illustrated inFIGS. 1, 2 and 4. For example, in the embodiments illustrated in FIG. 2with quantum dots of different dimensions, the plural quantum dots 211,212 of the first quantum dot emitting layer 21 may include 40% of indiumcontent; the plural quantum dots 231, 232 of the second quantum dotemitting layer 22 may include 45 of indium content; and the pluralquantum dots 231, 232 of the third quantum dot emitting layer 23 mayinclude 70% of indium content. As such, both the dimensions of thequantum dots and the indium content within the quantum dots may bemanipulated at the same time.

The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED according to thisinvention may be implemented in making yellow LED with an emissionwavelength at maximum luminous intensity falling within a range of530˜600 nm. It may also be implemented in making blue LED with anemission wavelength at maximum luminous intensity falling within a rangeof 400˜500 nm.

With reference to FIG. 5, a solid state white light emitting device 50according to this invention comprises: a first PCB 51, a second PCB 52,an Al_((1-x-y))In_(y)Ga_(x)N blue LED 53 and a broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54. TheAl_((1-x-y))In_(y)Ga_(x)N blue LED 53 and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54 are disposed overthe first PCB 51. The positive electrons supplied by the first PCB 51 tothe Al_((1-x-y))In_(y)Ga_(x)N blue LED 53 and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54 are electricallyconnected to a positive external power source. The negative electronssupplied by the second PCB 52 to the Al_((1-x-y))In_(y)Ga_(x)N blue LED53 and the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentaryLED 54 are electrically connected to a negative external power source.

By packaging the Al_((1-x-y))In_(y)Ga_(x)N blue LED 53 and thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54together, the mixing of blue light with blue-complimentary light wouldgenerate white light. In the laminar structure of the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54 as described in thefirst to fourth embodiments as described above, the emission wavelengthis increased by modulating the dimensions of the quantum dots or theindium content within the quantum dots to manipulate an uneven characterdistribution of the quantum dots. Accordingly, the solid state whitelight emitting device 50 according to this invention is capable ofgenerating white light with a high CRI index, high luminous intensityand capable of various color temperature modulation.

The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54illuminates yellow light with an emission wavelength at maximum luminousintensity falling within a range of 530˜600 nm, and FWHM within a rangeof 20˜150 μm. Since the broad-spectrum emission bandwidth covers thevisible spectrum that the human eyes are most sensitive to, the two LED53, 54 constructing the solid state white light emitting device 50 ofthis invention significantly enhance the luminous intensity of the whitelight. The distribution of the broad-spectrum of the LED 54 also furtherincreases the CRI index.

In packaging process, because the Al_((1-x-y))In_(y)Ga_(x)N blue LED 53and the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED54 implemented by the solid state white light emitting device 50 of thisinvention are both made of Al_((1-x-y))In_(y)Ga_(x)N, they have similardriving voltages, thermal stability, reliability and ESD impedancecharacteristics, for significantly reducing the packaging cost andimproving the reliability of the packaged devices while packaging theAl_((1-x-y))In_(y)Ga_(x)N blue LED 53 and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54 together.

Accordingly, the solid state white light emitting device of thisinvention may be implemented to serve as or to replace the white lightemitting device that is available in the commercial market, such as thewhite backlight of portable electronic products, vehicular lighting,landscape lighting, decorative lighting, and handheld lightingapparatus.

An embodiment is illustrated in FIG. 7, in which Curve 71 illustratesthe luminous intensity and bandwidth distribution of anAl_((1-x-y))In_(y)Ga_(x)N blue LED and Curve 72 illustrates the luminousintensity and bandwidth distribution of a broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED. As shown, the emissionwavelength of the Al_((1-x-y))In_(y)Ga_(x)N blue LED at its maximumluminous intensity (of 0.6) is 460 nm, and its FWHM (Full Width-HalfMaximum, that is, the wavelength bandwidth at an intensity of 0.3) is 20nm (450˜470 μm). The Al_((1-x-y))In_(y)Ga_(x)N blue LED is not featuredwith a broad-spectrum. The broad-spectrum Al_((1-x-y))In_(y)Ga_(x)Nblue-complimentary LED is implemented in generating yellow light, andmay be manipulated, such that the emission wavelength at its maximumluminous intensity (of 1) is 585 nm and its FWHM (Full Width-HalfMaximum, that is, the wavelength bandwidth at an intensity of 0.5) is 90nm (a bandwidth of 540˜630 nm) so as to feature the LED with abroad-spectrum. By packaging the Al_((1-x-y))In_(y)Ga_(x)N blue LED andthe broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N yellow LED together, themixing of blue light with yellow light would generate white light.

In the embodiment shown in FIG. 7, the luminous intensity (0.6) of theAl_((1-x-y))In_(y)Ga_(x)N blue LED is smaller than the luminousintensity (1) of the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N yellowLED, such that the white light generated by mixing the blue light withyellow light is one of a warm color temperature. Accordingly, the whitelight may be modulated into a state of warm color temperature, coldcolor temperature or the common daylight color temperature bymanipulating the scales and proportions of the maximum luminousintensity of the Al_((1-x-y))In_(y)Ga_(x)N blue LED and thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N yellow LED.

In FIG. 8, Curve 81 illustrates International commission on Illumination(CIE), and Curve 82 illustrates black body locus. A straight line 83connecting the two points representing the emission wavelength of 460 nmat the maximum luminous intensity of the blue light and the emissionwavelength 585 nm at the maximum luminous intensity of the yellow lightwould intersect the black body locus Curve 82 between values 2000 K and3000 K, evidencing that the solid state white light emitting devicedescribed in the above embodiment is capable of generating white lightof warm color temperature. However, since the emission wavelength of thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N yellow LED at the maximumluminous intensity falls within a range of 530˜600 nm, this inventionallow modulation of the white light into various color temperatures,such as a state of warm color temperature or cold color temperature(with black body locus greater than 10000 K).

As shown, FWHM of the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N yellowLED is 90 nm (540˜630=m), and the FWHM of the Al_((1-x-y))In_(y)Ga_(x)Nblue LED is 20 nm (450˜470 nm). A straight line 84 may be plotted byconnecting the two points representing wavelengths of 540 nm and 470 nm,and a straight line 85 may be plotted by connecting the two pointsrepresenting wavelengths of 630 nm and 450 nm. The area bounded by thestraight line 84 and straight line 85 indicates an extended white lightregion, evidencing that that the solid state white light emitting deviceaccording to this invention is capable of generating white light with anexcellent CRI.

As compared to the white light emitting device as described in the firstprior structure, the first prior white light emitting device mixes blueLED and yellow fluorescent powder to generate white light. Withreference to Curve 91 illustrates International commission onIllumination (CIE), and Curve 92 illustrates black body locus. Theemission wavelength of the blue LED in the prior white light emittingdevice at the maximum luminous intensity is 460 nm. The emissionwavelength of the yellow fluorescent powder at the maximum luminousintensity is 560 nm. A straight line 93 connecting the two pointsrepresenting these two wavelengths would intersect the black body locusCurve 92 around at 10000 K, evidencing that the prior white lightemitting device generates white light of warm color temperature. Inaddition, the prior white light emitting device is solely capable ofgenerating white light of warm color temperature but incapable of beingmodulated to generate white light of warm temperature due to itsstructural limitations.

To enhance the white light effect, the Al_((1-x-y))In_(y)Ga_(x)N blueLED 53 may take on the laminar structure as described in the first tofourth embodiments, rendering the emission wavelength of the blue LED atthe maximum luminous intensity to be within a range of 400˜500 nm, andits FWHM within a range of20100 nm. While both theAl_((1-x-y))In_(y)Ga_(x)N blue LED 53 and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 54 are featured with abroad-spectrum, the solid state white light emitting device according tothis invention allows better modulation of color temperature andprovides higher color saturation.

FIG. 6 a schematic view illustrates the solid state white light emittingdevice 60 according to this invention. The solid state white lightemitting device 60 comprises: an Al_((1-x-y))In_(y)Ga_(x)N blue LED 61,a broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 62, afirst electrode 64 and a second electrode 65. TheAl_((1-x-y))In_(y)Ga_(x)N blue LED 61 and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED 62 are packaged abovethe PCB mounted with the first electrode 64. To enhance the white lighteffect as generated, fluorescent powder 63 may be charged in thepackaging process. The fluorescent powder 63 may be red fluorescentpowder, green fluorescent powder or a mixture thereof. Accordingly,mixing of the red or green fluorescent powder with the blue light andblue-complimentary light would generate white light. The two LEDs 61, 62constructing the solid state white light emitting device 60 of thisinvention further enhance the luminous intensity of the white light andfeature the solid state white light emitting device 60 with a high CRIindex.

In addition, the solid state white light emitting device according tothis invention may be made by packaging a red, a blue and a green LEDtogether, such that mixing of blue light, red light with the green lightwould generate white light. The solid state white light emitting devicecomprises: a broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue LED, abroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N red LED and a broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N green LED. The broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N green, blue and red LED each take on thelaminar structure as described in the first to fourth embodiments tofeature the LED with a broad-spectrum.

The emission wavelength of the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)Nred LED at the maximum luminous intensity falls within a range of560˜650=m. The emission wavelength of the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N green LED at the maximum luminous intensityfalls with a range of 490˜560 μm. The emission wavelength of thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue LED at the maximumluminous intensity falls within a range of 400˜490 μm. The FWHM of boththe broad-spectrum red LED and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N green LED falls with a range of 20˜150 nm. TheFWHM of the Al_((1-x-y))In_(y)Ga_(x)N blue LED falls with a range 20˜100nm. The solid state white light emitting device made by packaging theabove red, blue and green LED together would improve the luminousintensity of the white light emitting device while allowing modulationof the color temperature and CRI.

The solid state white light emitting device of this invention mayalternatively be made by packaging a UVA LED, blue light fluorescentpowder and a broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentaryLED together, such that mixing of the blue light fluorescent powder withthe blue-complimentary light would generate white light. The 4additionof the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LEDenhances the overall luminous intensity, thereby eliminating thedrawback of insufficient luminous intensity found in the prior art thatimplements a single UVA LED. In addition, the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED taking on the laminarstructure described in the first to fourth embodiments would feature thewhite light emitting device with a broad-spectrum and allow modulationof the color temperature and CRI.

In the above embodiment, in addition to the blue light fluorescentpowder, red fluorescent powder, green fluorescent powder or a mixturethereof may be further added, such that mixing of the red or greenfluorescent powder with the blue light fluorescent powder andblue-complimentary would generate white light, so as to allow furthermodulation of the color temperature and CRI.

It is understood that the invention may be embodied in other formswithout departing from the spirit thereof. Thus, the present examplesand embodiments are to be considered in all respects as illustrative andnot restrictive, and the invention is not to be limited to the detailsgiven herein.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

1. A broad-spectrum Al_((1-x-y))In_(y)Ga_(x)N LED, comprising: asubstrate; a buffer layer, disposed over the substrate; an N-typecladding layer, disposed over the buffer layer; at least one quantum dotemitting layer, disposed over the N-type cladding layer, the quantum dotemitting layer including plural quantum dots with an uneven characterdistribution so as to increase FWHM of emission wavelength of thequantum dot emitting layer; and a P-type cladding layer, disposed overthe quantum dot emitting layer.
 2. The LED of claim 1, wherein thequantum dots are of different dimensions to result in the unevencharacter distribution of the quantum dots.
 3. The LED of claim 1,wherein indium content of the quantum dots is different to result in theuneven character distribution of the quantum dots.
 4. The LED of claim2, wherein indium content of the quantum dots is different to result inthe uneven character distribution of the quantum dots.
 5. The LED ofclaim 1, wherein the quantum dot emitting layer further includes a firstbarrier layer and a second barrier layer, the first barrier layer beingdisposed under the quantum dots, the second barrier layer being disposedover the quantum dots, the first barrier layer and the second barrierlayer each having an energy band gap that is greater than an energy bandgap of the quantum dots.
 6. The LED of claim 1, comprising pluralquantum dot emitting layers, the quantum dot emitting layers each havingplural quantum dots and an uneven character so as to increase FWHM ofemission wavelength of the quantum dot emitting layer.
 7. The LED ofclaim 6, wherein the quantum dots of the quantum dot emitting layers areof different dimensions to result in the uneven character distributionof the quantum dot emitting layer.
 8. The LED of claim 7, wherein indiumcontent of the quantum dots of the quantum dot emitting layers isdifferent to result in the uneven character distribution of the quantumdot emitting layer.
 9. The LED of claim 6, wherein indium content of thequantum dots of the quantum dot emitting layers is different to resultin the uneven character distribution of the quantum dot emitting layer.10. The LED of claim 6, wherein the quantum dot emitting layers eachfurther comprise a first barrier layer and a second barrier layer, thefirst barrier layer being disposed under the quantum dots, the secondbarrier layer being disposed over the quantum dots, the first barrierlayer and the second barrier layer each having an energy band gap beinggreater than an energy band gap of the quantum dots.
 11. The LED ofclaim 10, wherein two adjacent barrier layers are of an identicallaminar structure so as to omit one of the two adjacent barrier layersto become a single barrier layer.
 12. The LED of claim 10, wherein acontent proportion of laminar structure of the first barrier layer orthe second barrier layer is manipulated such that the first barrierlayer or the second barrier layer includes plural barrier layers ofdifferent content proportions.
 13. A solid state white light emittingdevice, comprising: an Al_((1-x-y))In_(y)Ga_(x)N blue LED; and abroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED,packaged with the Al_((1-x-y))In_(y)Ga_(x)N blue LED to mix blue lightand blue-complimentary light for generating white light, thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LEDincluding: a substrate; a buffer layer, disposed over the substrate; anN-type cladding layer, disposed over the buffer layer; at least onequantum dot emitting layer, disposed over the N-type cladding layer, thequantum dot emitting layer including plural quantum dots with an unevencharacter distribution so as to increase FWHM of emission wavelength ofthe quantum dot emitting layer; and a P-type cladding layer, disposedover the quantum dot emitting layer.
 14. The solid state white lightemitting device of claim 13, wherein the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED has an FWHM fallingwith a range of 20˜150 nm.
 15. The solid state white light emittingdevice of claim 13, wherein the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)Nblue-complimentary LED has an emission wavelength at maximum luminousintensity falling within a range of 530˜600 nm.
 16. The solid statewhite light emitting device of claim 13, wherein theAl_((1-x-y))In_(y)Ga_(x)N blue LED includes: a substrate; a bufferlayer, disposed over the substrate; an N-type cladding layer, disposedover the buffer layer; at least one quantum dot emitting layer, disposedover the N-type cladding layer, the quantum dot emitting layer includingplural quantum dots with an uneven character distribution so as toincrease FWHM of emission wavelength of the quantum dot emitting layer;and a P-type cladding layer, disposed over the quantum dot emittinglayer.
 17. The solid state white light emitting device of claim 16,wherein the Al_((1-x-y))In_(y)Ga_(x)N blue LED has an emissionwavelength at maximum luminous intensity falling within a range of400˜500 nm.
 18. The solid state white light emitting device of claim 16,wherein the Al_((1-x-y))In_(y)Ga_(x)N blue LED has FWHM falling within arange of 20˜100 nm.
 19. The solid state white light emitting device ofclaim 13, further comprising red fluorescent powder, packaged with theAl_((1-x-y))In_(y)Ga_(x)N blue LED and the broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED, to mix the redfluorescent powder with the blue light and blue-complimentary light forgenerating white light.
 20. A solid state white light emitting device,comprising: a UVA LED; blue light fluorescent powder; a broad-spectrumAl_((1-x-y))In_(y)Ga_(x)N blue-complimentary LED, packaged with the UVALED and blue light fluorescent powder, to mix the blue light fluorescentpowder and blue-complimentary light for generating white light, thebroad-spectrum Al_((1-x-y))In_(y)Ga_(x)N blue-complimentary LEDincluding: a substrate; a buffer layer, disposed over the substrate; anN-type cladding layer, disposed over the buffer layer; at least onequantum dot emitting layer, disposed over the N-type cladding layer, thequantum dot emitting layer including plural quantum dots with an unevencharacter distribution so as to increase FWHM of emission wavelength ofthe quantum dot emitting layer; and a P-type cladding layer, disposedover the quantum dot emitting layer.
 21. The solid state white lightemitting device of claim 20, further comprising red fluorescent powder,packaged with the broad-spectrum Al_((1-x-y))In_(y)Ga_(x)Nblue-complimentary LED, the UVA LED and blue light fluorescent powder,to mix the red fluorescent powder, blue light fluorescent powder andblue-complimentary light for generating white light.